BACKGROUND OF THE INVENTION
Field of the Invention
[0001] This invention relates generally to passenger and light truck tires and more particularly
to treads and materials from which they are made.
Description of the Related Art
[0002] It is known in the industry that tire designers must compromise on certain characteristics
of the tires they are designing. Changing a tire design to improve one characteristic
of the tire will often result in a compromise,
i.e., an offsetting decline in another tire characteristic. One such compromise exists
between wet braking and snow traction. Wet braking may be improved by increasing filler
loading, decreasing filler particle size and increasing the mix glass transition temperature
(Tg). However, these actions typically result in a loss of snow traction performance
that is known to be improved by, for example, decreasing filler loading, increasing
filler particle size and decreasing mix Tg.
[0003] Tire designers and those conducting research in the tire industry search for materials
and tire structures that can break some of the known compromises. It would be desirable
to provide new tire designs that break the compromise between wet and snow traction.
SUMMARY OF THE INVENTION
[0004] Particular embodiments of the present invention include a tread for a tire that is
manufactured from a rubber composition that is based upon a cross-linkable elastomer
composition. One such disclosed rubber composition is based upon an elastomer composition
that includes, per 100 phr, 100 phr of two elastomer types including at least 50 phr
of a styrene-butadiene copolymer (SBR) with a polybutadiene (BR) as the remainder.
Such compositions may further include between 90 phr and 150 phr of a silica filler.
[0005] Also included in such elastomer compositions is a plasticizing system that includes
a plasticizing resin having a glass transition temperature (Tg) of at least 25 °C
and a plasticizing liquid. The plasticizing system is added in an effective amount
to provide the cured rubber composition with a shear modulus G* measured at 60 °C
of between 0.7 MPa and 1.6 MPa and a Tg of between -35 °C and 0 °C.
[0006] The cross-linkable elastomer composition further includes a peroxide curing system
for curing the elastomer composition. In some embodiments a non-ionic curing coagent
may also be included as a component of the elastomer composition.
[0007] The cross-linkable elastomer composition further includes an organosilane coupling
agent that in particular embodiments may include those having no sulfur or having
a tetrasulfide, a trisulfide, a disulfide or a mercapto moiety.
[0008] The foregoing and other objects, features and advantages of the invention will be
apparent from the following more detailed descriptions of particular embodiments of
the invention.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
[0009] Particular embodiments of the present invention include treads that have improved
traction,
i.e., improved performance in both wet and damp braking and in snow traction. Also included
are embodiments of tires having such treads. This improved traction and braking performance
has been achieved by forming unique tire treads from a rubber composition having a
high loading of silica coupled with an effective amount of a plasticizing system added
to adjust the shear modulus G* measured at 60 °C to be between 0.6 MPa and 1.5 MPa
and a Tg of between -35 °C and 0 °C and cured with a peroxide curing system. Such
tires are particularly useful as snow tires or as all-weather tires for passenger
cars and/or light trucks and also for summer tires.
[0010] As used herein, "phr" is parts per hundred parts of rubber by weight and is a common
measurement in the art wherein components of a rubber composition are measured relative
to the total weight of rubber in the composition,
i.e., parts by weight of the component per 100 parts by weight of the total rubber(s) in
the composition.
[0011] As used herein, elastomer and rubber are synonymous terms.
[0012] As used herein, "based upon" is a term recognizing that embodiments of the present
invention are made of vulcanized or cured rubber compositions that were, at the time
of their assembly, uncured. The cured rubber composition is therefore "based upon"
the uncured rubber composition. In other words, the cross-linked rubber composition
is based upon or comprises the constituents of the cross-linkable rubber composition.
[0013] As is known generally, a tire tread is the road-contacting portion of a vehicle tire
that extends circumferentially about the tire. It is designed to provide the handling
characteristics required by the vehicle;
e.g., traction, dry braking, wet braking, cornering and so forth - all being preferably
provided with a minimum amount of noise being generated and at a low rolling resistance.
[0014] Treads of the type that are disclosed herein include tread elements that are the
structural features of the tread that contact the ground. Such structural features
may be of any type or shape, examples of which include tread blocks and tread ribs.
Tread blocks have a perimeter defined by one or more grooves that create an isolated
structure in the tread while a rib runs substantially in the longitudinal (circumferential)
direction and is not interrupted by any grooves that run in the substantially lateral
direction or any other grooves that are oblique thereto.
[0015] The radially outermost faces of these tread elements make up the contact surface
of the tire tread - the actual surface area of the tire tread that is adapted for
making contact with the road as the tire rotates. The total contact surface of the
tire tread is therefore the total surface area of all the radially outermost faces
of the tread elements that are adapted for making contact with the road.
[0016] Suitable compositions for making the treads disclosed herein include a particular
rubber component, a plasticizing system, reinforcement filler and a peroxide curing
system. The rubber components included in the rubber composition are highly unsaturated
rubbers that include two types - styrene-butadiene copolymers (SBR) and polybutadienes
(BR), both quite commonly used in the tire industry. Polybutadienes are useful in
many rubber articles and are homopolymers of conjugated 1,3-butadiene. The polybutadienes
are particularly useful in maintaining a desirable wear characteristic of the tread
since the addition of BR typically improves the wear property.
[0017] SBR is a copolymer of styrene and 1, 3-butadiene and is one of the most commonly
used synthetic rubbers. The microstructure of SBR is typically described in terms
of the amount of bound styrene and the form of the butadiene portion of the polymer.
A typical SBR that is often suitable for use in tires is around 25 wt. % bound styrene.
Materials having a very high content of bound styrene,
e.g., around 80 wt. %, are identified as high styrene resins and are not suitable as an
elastomer for manufacturing treads. Particular embodiments of the present invention
may utilize an SBR having a bound styrene content of between 3 wt. % and 40 wt. %
or alternatively between 10 wt. % and 35 wt. %, between 15 wt. % and 30 wt. % or between
20 wt. % and 40 wt. % bound styrene.
[0018] Because of the double bond present in the butadiene portion of the SBR, the butadiene
portion is made up of three forms:
cis-1,4,
trans-1,4 and vinyl-1,2. In particular embodiments, the SBR materials may be characterized
as having a high
trans-1,4 content of at least 30 wt. % or alternatively between 30 wt. % and 70 wt. %,
between 35 wt. % and 55 wt. % or between 35 wt. % and 40 wt. %.
[0019] Methods for determining the microstructure of the butadiene portion of the SBR materials
are well known to those having ordinary skill in the art and include, for example,
NMR methods and infrared spectroscopy methods. In one suitable NMR spectroscopy method,
a carbon-13 NMR analyses may be performed using, for example, a Bruker AM250 spectrometer.
The nominal frequency of carbon-13 is 62.9 MHz and the spectra are recorded without
the "nuclear Overhauser effect" (NOE) to ensure quantitative results. The spectral
width is 240 ppm. The angle pulse used is a 90° pulse, the duration of which is 5
µs. Low-power decoupling with a wide proton band are used to eliminate scalar
1H-carbon-13 coupling during carbon-13 acquisition. The sequence repetition time is
4 seconds. The number of transients accumulated to increase the signal/noise ratio
is 8192. The spectra are calibrated against the CDCl
3 band at 77 ppm.
[0020] The rubber compositions useful for the treads disclosed herein may include a functionalized
SBR component. Functionalized rubbers,
i.e., those appended with active moieties, are well known in the industry. The elastomers
may be functionalized by attaching these active moieties to the polymer backbone,
along the branches of the polymer or at the branch ends of the polymer. Examples of
functionalized elastomers include silanol or polysiloxane functionalized elastomers,
examples of which may be found in
US Patent No. 6,013,718, which is hereby fully incorporated by reference. Other examples of functionalized
elastomers include those having alkoxysilane groups as described in
US 5,977,238, carboxylic groups as described in
US 6,815,473, polyether groups as described in
US 6,503,973 or amino groups as described in
US 6,800,582 and are all incorporated herein by reference.
[0021] In particular embodiments of the present invention, the SBR is a functionalized elastomer
having functional moieties attached to at least a portion of the total number of branch
ends or alternatively, along the branches of the butadiene portion of the polymer.
Such functional moieties may include, for example, amino groups, silanol groups, alkoxysilane
groups, carboxylic groups or polyether groups. In particular embodiments, the functional
moieties may be selected from amino groups, silanol groups or alkoxysilane groups
or alternatively, just silanol groups. In particular embodiments, the functionalized
SBR may include a mixture of two or more different such functionalized SBR's or limited
to one of the functionalized SBR's.
[0022] The rubber compositions disclosed herein may include between 50 phr and 90 phr of
the SBR or alternatively between 50 phr and 80 phr, between 55 phr and 80 phr or between
60 phr and 75 phr. Likewise the rubber compositions may include between 10 phr and
50 phr of the polybutadiene rubber or alternatively between 20 phr and 50 phr, between
20 phr and 45 phr or between 20 phr and 30 phr.
[0023] In addition to the rubber components described above, the rubber composition suitable
for the tire treads disclosed herein may further include a plasticizing system. The
plasticizing system provides both an improvement to the processability of the rubber
mix and a means for adjusting the rubber composition's dynamic shear modulus and glass
transition temperature. Suitable plasticizing systems include both a plasticizing
liquid and a plasticizing resin to achieve the desired braking and snow traction characteristics
of the tread.
[0024] Suitable plasticizing liquids may include any liquid known for its plasticizing properties
with diene elastomers. At room temperature (23 °C), these liquid plasticizers, or
these oils, of varying viscosity are liquid as opposed to the resins that are solid.
Examples include those derived from petroleum stocks, those having a vegetable base
and combinations thereof. Examples of oils that are petroleum based include aromatic
oils, paraffinic oils, naphthenic oils, MES oils, TDAE oils and so forth as known
in the industry. Also known are liquid diene polymers, the polyolefin oils, ether
plasticizers, ester plasticizers, phosphate plasticizers, sulfonate plasticizers and
combinations of liquid plasticizers.
[0025] Examples of suitable vegetable oils include sunflower oil, soybean oil, safflower
oil, corn oil, linseed oil and cotton seed oil. These oils and other such vegetable
oils may be used singularly or in combination. In some embodiments, sunflower oil
having a high oleic acid content (at least 70 weight percent or alternatively, at
least 80 weight percent) is useful, an example being AGRI-PURE 80, available from
Cargill with offices in Minneapolis, MN. In particular embodiments of the present
invention, the selection of suitable plasticizing oils is limited to a vegetable oil
having high oleic acid content.
[0026] The amount of plasticizing liquid useful in any particular embodiment of the present
invention depends upon the particular circumstances and the desired result. In general,
for example, the plasticizing liquid may be present in the rubber composition in an
amount of between 5 phr and 60 phr or alternatively, between 10 phr and 50 phr, between
10 phr and 40 phr, between 10 phr and 30 phr, between 10 phr and 50 phr or between
12 phr and 30 phr. Since both a plasticizing liquid and a plasticizing hydrocarbon
resin are included in the plasticizing system, the amount of both types of plasticizers
is adjusted as described below to obtain the desired physical characteristics of the
tread.
[0027] A plasticizing hydrocarbon resin is a hydrocarbon compound that is solid at ambient
temperature (
e.g., 23 °C) as opposed to liquid plasticizing compounds, such as plasticizing oils. Additionally
a plasticizing hydrocarbon resin is compatible,
i.e., miscible, with the rubber composition with which the resin is mixed at a concentration
that allows the resin to act as a true plasticizing agent,
e.g., at a concentration that is typically at least 5 phr.
[0028] Plasticizing hydrocarbon resins are polymers/oligomers that can be aliphatic, aromatic
or combinations of these types, meaning that the polymeric base of the resin may be
formed from aliphatic and/or aromatic monomers. These resins can be natural or synthetic
materials and can be petroleum based, in which case the resins may be called petroleum
plasticizing resins, or based on plant materials. In particular embodiments, although
not limiting the invention, these resins may contain essentially only hydrogen and
carbon atoms.
[0029] The plasticizing hydrocarbon resins useful in particular embodiment of the present
invention include those that are homopolymers or copolymers of cyclopentadiene (CPD)
or dicyclopentadiene (DCPD), homopolymers or copolymers of terpene, homopolymers or
copolymers of C
5 cut and mixtures thereof.
[0030] Such copolymer plasticizing hydrocarbon resins as discussed generally above may include,
for example, resins made up of copolymers of (D)CPD/ vinyl-aromatic, of (D)CPD/ terpene,
of (D)CPD/ C
5 cut, of terpene/ vinyl-aromatic, of C
5 cut/ vinyl-aromatic and of combinations thereof.
[0031] Terpene monomers useful for the terpene homopolymer and copolymer resins include
alpha-pinene, beta-pinene and limonene. Particular embodiments include polymers of
the limonene monomers that include three isomers: the L-limonene (laevorotatory enantiomer),
the D-limonene (dextrorotatory enantiomer), or even the dipentene, a racemic mixture
of the dextrorotatory and laevorotatory enantiomers.
[0032] Examples of vinyl aromatic monomers include styrene, alpha- methylstyrene, ortho-,
meta-, para-methylstyrene, vinyl-toluene, para-tertiobutylstyrene, methoxystyrenes,
chloro-styrenes, vinyl-mesitylene, divinylbenzene, vinylnaphthalene, any vinyl-aromatic
monomer coming from the C
9 cut (or, more generally, from a C
8 to C
10 cut). Particular embodiments that include a vinyl-aromatic copolymer include the
vinyl-aromatic in the minority monomer, expressed in molar fraction, in the copolymer.
[0033] Particular embodiments of the present invention include as the plasticizing hydrocarbon
resin the (D)CPD homopolymer resins, the (D)CPD/ styrene copolymer resins, the polylimonene
resins, the limonene/ styrene copolymer resins, the limonene/ D(CPD) copolymer resins,
C
5 cut/ styrene copolymer resins, C
5 cut/ C
9 cut copolymer resins, and mixtures thereof.
[0034] Commercially available plasticizing resins that include terpene resins suitable for
use in the present invention include a polyalphapinene resin marketed under the name
Resin R2495 by Hercules Inc. of Wilmington, DE. Resin R2495 has a molecular weight
of about 932, a softening point of about 135°C and a glass transition temperature
of about 91°C. Another commercially available product that may be used in the present
invention includes DERCOLYTE L120 sold by the company DRT of France. DERCOLYTE L120
polyterpene-limonene resin has a number average molecular weight of about 625, a weight
average molecular weight of about 1010, an Ip of about 1.6, a softening point of about
119°C and has a glass transition temperature of about 72° C. Still another commercially
available terpene resin that may be used in the present invention includes SYLVARES
TR 7125 and/or SYLVARES TR 5147 polylimonene resin sold by the Arizona Chemical Company
of Jacksonville, FL. SYLVARES 7125 polylimonene resin has a molecular weight of about
1090, has a softening point of about 125° C, and has a glass transition temperature
of about 73°C while the SYLVARES TR 5147 has a molecular weight of about 945, a softening
point of about 120 °C and has a glass transition temperature of about 71° C.
[0035] Other suitable plasticizing hydrocarbon resins that are commercially available include
C
5 cut/ vinyl-aromatic styrene copolymer, notably C
5 cut / styrene or C
5 cut / C
9 cut from Neville Chemical Company under the names SUPER NEVTAC 78, SUPER NEVTAC 85
and SUPER NEVTAC 99; from Goodyear Chemicals under the name WINGTACK EXTRA; from Kolon
under names HIKOREZ T1095 and HIKOREZ T1100; and from Exxon under names ESCOREZ 2101
and ECR 373.
[0036] Yet other suitable plasticizing hydrocarbon resins that are limonene/styrene copolymer
resins that are commercially available include DERCOLYTE TS 105 from DRT of France;
and from Arizona Chemical Company under the name ZT115LT and ZT5100.
[0037] It may be noted that the glass transition temperatures of plasticizing resins may
be measured by Differential Scanning Calorimetry (DSC) in accordance with ASTM D3418
(1999). In particular embodiments, useful resins may be have a glass transition temperature
that is at least 25° C or alternatively, at least 40° C or at least 60° C or between
25° C and 95° C, between 40° C and 85° C or between 60° C and 80° C.
[0038] The amount of plasticizing hydrocarbon resin useful in any particular embodiment
of the present invention depends upon the particular circumstances and the desired
result and may be present in an amount of between 5 phr and 100 phr or alternatively,
between 30 phr and 60 phr, between 20 phr and 60 phr, between 30 phr and 90 phr, between
30 phr and 55 phr or between 35 phr and 60 phr. As noted above, since both a plasticizing
liquid and a plasticizing hydrocarbon resin are included in the plasticizing system,
the amount of both types of plasticizers are adjusted as described below to obtain
the desired physical characteristics of the tread to improve both the snow traction
and braking properties.
[0039] The amount of the plasticizing system is adjusted to provide the rubber composition
with a glass transition temperature of between -35 °C and 0 °C and a dynamic modulus
G* at 60 °C of between 0.6 MPa and 1.5 MPa or alternatively between 0.65 MPa and 1.2
MPa, between 0.65 MPa and 1.1 MPa, between 0.65 MPa and 1.0 MPa or between 0.7 MPa
and 1.0 MPa, both measured in accordance with ASTM D5992-96. As such, the ratio of
the amount of liquid plasticizer (phr) to the amount of plasticizing resin (phr) may
be adjusted to achieve the desired physical properties of the rubber composition so
that the surprising break in the braking-snow traction compromise is achieved. Such
ratios may range from between 0.1 and 0.7 or alternatively between 0.2 and 0.5, between
0.2 and 0.6 or between 0.3 and 0.6.
[0040] The rubber compositions disclosed herein are suitable for use in the manufacture
of treads and as known to one skilled in the art, the Tg of the cured rubber composition
may be adjusted to provide a tread for a tire that is more suitable for a given season.
As such the Tg of the rubber compositions may be adjusted around the broad range mentioned
above using the plasticizers disclosed to provide a Tg of between -35 °C and -25 °C
for winter tires, between -30 °C and -17 °C for all-season tires and between -17 °C
and 0 °C for summer tires.
[0041] In addition to the rubber components and the plasticizing system described above,
the rubber compositions suitable for the tire treads disclosed herein may further
include a silica reinforcing filler. Reinforcing fillers are used extensively in tires
to provide desirable characteristics such as tear strength, modulus and wear. The
silica may be any reinforcing silica known to one having ordinary skill in the art,
in particular any precipitated or pyrogenic silica having a BET surface area and a
specific CTAB surface area both of which are less than 450 m
2/g or alternatively, between 30 and 400 m
2/g. Particular embodiments include a silica having a CTAB of between 80 and 200 m
2/g, between 100 and 190 m
2/g, between 120 and 190 m
2/g or between 140 and 180 m
2/g. The CTAB specific surface area is the external surface area determined in accordance
with Standard AFNOR-NFT-45007 of November 1987.
[0042] Particular embodiments of the rubber compositions used in the tire treads of the
passenger and light truck vehicles have a BET surface area of between 60 and 250 m
2/g or alternatively, of between 80 and 200 m
2/g. The BET specific surface area is determined in known manner, in accordance with
the method of Brunauer, Emmet and Teller described in "
The Journal of the American Chemical Society", vol. 60, page 309, February 1938, and corresponding to Standard AFNOR-NFT-45007 (November 1987).
[0043] The silica used in particular embodiments may be further characterized as having
a dibutylphthlate (DHP) absorption value of between 100 and 300 ml/100 g or alternatively
between 150 and 250 ml/100 g.
[0044] Highly dispersible precipitated silicas (referred to as "HD") are used exclusively
in particular embodiments of the disclosed rubber composition, wherein "highly dispersible
silica" is understood to mean any silica having a substantial ability to disagglomerate
and to disperse in an elastomeric matrix. Such determinations may be observed in known
manner by electron or optical microscopy on thin sections. Examples of known highly
dispersible silicas include, for example, Perkasil KS 430 from Akzo, the silica BV3380
from Degussa, the silicas Zeosil 1165 MP and 1115 MP from Rhodia, the silica Hi-Sil
2000 from PPG and the silicas Zeopol 8741 or 8745 from Huber.
[0045] Particular embodiments of the present invention include little or no carbon black
or other reinforcement fillers. For those embodiments that include adding a silane
coupling agent that is commercially available on a carbon black substrate, up to about
50 wt% of the commercial coupling agent weight is carbon black. The rubber compositions
having such amounts of carbon black may be characterized as having essentially no
carbon black. Some embodiments may include up to 10 phr, or up to 5 phr of carbon
black just to provide a typical black coloring of the rubber composition.
[0046] The amount of silica added to the rubber composition disclosed herein is between
90 phr and 150 phr or alternatively between 95 phr and 145 phr, between 100 phr and
135 phr or between 105 phr and 140 phr.
[0047] In addition to the silica added to the rubber composition, a proportional amount
of a silane coupling agent is also added to the rubber composition. Such coupling
agent is added, for example, at between 5% and 10% of the total amount of silica.
The silane coupling agent is an organosilicon (also called an organosilane) compound
that reacts with the silanol groups of the silica during mixing and with the elastomers
during vulcanization to provide improved properties of the cured rubber composition.
A suitable coupling agent is one that is capable of establishing a sufficient chemical
and/or physical bond between the inorganic filler and the diene elastomer, which is
at least bifunctional, having, for example, the simplified general formula "Y-T-X",
in which: Y represents a functional group ("Y" function) which is capable of bonding
physically and/or chemically with the inorganic filler, such a bond being able to
be established, for example, between a silicon atom of the coupling agent and the
surface hydroxyl (OH) groups of the inorganic filler (for example, surface silanols
in the case of silica); X represents a functional group ("X" function) which is capable
of bonding physically and/or chemically with the diene elastomer, for example by means
of a sulfur atom or a vinyl, an epoxy group or a methacryloxy group; T represents
a divalent organic group making it possible to link Y and X. As in known in the art,
the intervening divalent group T is not essential, though it is preferable. For example,
in the case of a coupling agent having a vinyl group as the X function, the vinyl
group may be attached directly to the Y group without the intervening divalent group
T.
[0048] Coupling agents are very well known in the art and the examples that follow are not
meant to limit the rubber compositions disclosed herein to include only those coupling
agents that are listed below as examples. However, particular embodiments of the rubber
compositions are limited, as explained below, only to those coupling agents that have
limited or no amounts of sulfur included in them. While excellent physical properties
are achieved with the peroxide cured rubber compositions having higher levels of sulfur,
even better properties are obtained when the amount of sulfur in the coupling agents
is limited.
[0049] In general, examples of sulfur-containing organosilicon silane coupling agents that
are suitable for particular embodiments of the rubber formulations disclosed herein
that are not limited to a maximum sulfur level include 3,3'-bis(triethoxysilylpropyl)disulfide
(TESPD) and 3,3'-bis(triethoxysilylpropyl) tetrasulfide (TESPT). Both of these are
available commercially from Degussa as X75-S and X50-S respectively, though not in
pure form. Both of these commercially available products include the active component
mixed 50-50 by weight with a N330 carbon black. Other examples of suitable silane
coupling agents include 2,2'-bis(triethoxysilylethyl)tetrasulfide, 3,3'-bis(tri-t-butoxysilylpropyl)disulfide
and 3,3'-bis(di-t-butylmethoxysilylpropyl)tetrasulfide.
[0050] As noted above, is has been further discovered that when the coupling agent includes
a sulfur chain greater than about 3 sulfur atoms, the benefits of the peroxide cured
rubber compositions disclosed herein are not as great as when the coupling agent has
no more than about 3 sulfur atoms or even no sulfur atoms as, for example, in those
coupling agents that may include vinyl or epoxy groups for bonding to the elastomer
instead of sulfur.
[0051] Therefore particular embodiments of the peroxide cured rubber compositions disclosed
herein have coupling agents of the same general Y-T-X form except that the X function
that is capable of bonding with the diene elastomer is limited to moieties that include
no sulfur and those that may include a mono-sulfur moiety or a sulfur chain that is
no greater than on average about 3 sulfur atoms long or alternatively no greater than
on average about 2.5 or no greater than on average about 2 sulfur atoms in length.
Such coupling agents are well known to those skilled in the art and the following
lists include examples of such suitable coupling agents. Controlling the sulfur average
chain length of such compounds is well-known and such descriptions may be found, for
example, in publication
WO2007/061550.
[0052] Suitable coupling agents having sulfur chains of no more than on average about 3
sulfur atoms long include 3,3'-bis(triethoxysilylpropyl)disulfide (TESPD), 3,3'-bis(triethoxysilylpropyl)trisulfides,
2,2'-bis (dimethylmethoxysilylethyl) disulfide, 3.3'-bis(propyldiethoxysilylpropyl)
disulfide and more generally, of bis(mono(C
1-C
4)alkoxydi-(C
1-C
4)alkylsilylpropyl)disulfides and/or trisulfides. Such organosilicon coupling agents
are well known and these and others of this type may be found, for example, in
US patent 3978103. Other examples may include bis(3-hydroxydimethylsilyl)propyl disulfide and bis(2-hydroxydimethylsilyl)ethyl
disulfide that are monohydroxysilane disulfides.
[0053] When the sulfur atom is a mono-sulfur, the coupling agent may be a mercaptosilane,
wherein the X function is a thiol (SH) functional group. An example of such a coupling
agent is 3-mercaptopropyltrimethoxysilane, which is available from Evonik as DYNASYLAN
MTMO. Another example may include 2-mercaptoethyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane
and 2-mercaptodimethylmethoxysilane. Examples of such coupling agents are available
from Shin-Etsu Chemical Co, Ltd. of Tokyo. More generally such coupling agents are
described in
US patent 6849754.
[0054] As noted, the coupling agents are not limited only to those with sulfur as the X
function of the coupling agent. One well known example of such coupling agents are
those that include, for example, an epoxy group or a vinyl group as the X function.
Examples having epoxy functional groups include 3-Glycidoxypropyl methyldimethoxy
silane, 3-Glycidoxypropyl trimethoxysilane, which are available from Shin-Etsu Chemical
Co, Ltd. Of Tokyo, Japan. Vinyl coupling agents may include, for example, vinyltrimethoxysilane
and vinyltriethoxysilane, also available from Shin-Etsu Chemical Co, Ltd. Examples
having methacryoxy groups may include, for example, 3-methacryloxypropyl methyldimethoxysilane
and 3-methacryloxypropyl trimethoxysilane, also available from Shin-Etsu Chemical
Co. Ltd.
[0055] In addition to the rubber components, the plasticizing system and the reinforcing
filler described above, the rubber compositions suitable for the tire treads disclosed
herein may further be cured by a peroxide curing system. The peroxide curing system,
or vulcanization system, provides the cross-linking mechanism for the formation of
covalent bonds between the elastomer chains resulting from the decomposition of the
peroxide to form radicals and the subsequent crosslink-forming reactions. The peroxide
curing system is necessary to provide the break in the compromise between the braking
and snow traction as discussed above.
[0056] Examples of suitable peroxide curing agents include di-cumyl peroxide; tert-butyl
cumyl peroxide; 2,5-dimethyl-2,5 bis(tertbutyl peroxy)hexyne-3; bis(tert-butyl peroxy
isopropyl)benzene; 4,4-di-tert-butyl peroxy N-butyl valerate; 1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane;
bis-(tert-butyl peroxy)-diisopropyl benzene; t-butyl perbenzoate; di-tert-butyl peroxide;
2,5-dimethyl-2,5-di-tert-butylperoxide hexane, as well as other peroxides known to
those having ordinary skill in the art and combinations thereof. Such peroxides are
available, for example, as VUL-CUP-R, which is α,α'-bis-(tert-butyl peroxy)-diisopropyl
benzene and DI CUP, which is di-cumyl peroxide, both available from Arkema having
offices in Philadelphia, PA.
[0057] The peroxide curing agent may be added to the rubber composition in an effective
amount such as between 0.8 phr and 2.4 phr of active peroxide or alternatively between
1 phr and 2 phr. Since the peroxide products often include inactive ingredients added
to the active peroxide, the amount of peroxide disclosed is the amount of active peroxide
that should be added to the useful rubber compositions.
[0058] In addition to the peroxide curing agent, a coagent may also be included in the peroxide
curing package for particular embodiments of the rubber compositions disclosed herein.
Coagents affect the cross-linking efficiency and may improve the properties of the
cured rubber compositions.
[0059] Useful curing coagents include those that are non-ionic. Such coagents are known
to typically contribute to the state of the cure of the vulcanized rubber and form
radicals typically through hydrogen abstraction. Examples of non-ionic coagents include,
for example, allyl-containing cyanurates, isocyanurates and phthalates, homopolymers
of dienes and copolymers of dienes and vinyl aromatics, such as triallyl cyanurates,
triallyl isocyanurate, 90% vinyl polybutadiene and 70% vinyl styrene-butadiene copolymer.
RICON 153 is available from Cray Valley (with offices in Exton, PA) and is 85% 1,
2 vinyl polybutadiene, a useful non-ionic coagent having a number average MW of 4700.
Any of these coagents may be used singly or in combinations with one or more of the
others.
[0060] It has been shown that polar coagents are not useful for the present invention and
they are excluded from the rubber compositions disclosed herein. These polar coagents
typically increase both the rate and state of the cure and form very reactive radicals
through addition reactions. Examples of these polar coagents include multifunctional
acrylate and methacrylate esters and dimaleimides, such as the zinc salts of acrylic
and methacrylic acid, ethylene glycol diacrylate, trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate and N, N'-m-phenylene dimaleimides.
[0061] The non-ionic coagents may be added to particular embodiments of the rubber compositions
disclosed herein in an amount of between 1 phr and 7 phr or alternatively, between
2 phr and 6 phr or between 3 phr and 5 phr.
[0062] Other additives can be added to the rubber compositions disclosed herein as known
in the art. Such additives may include, for example, some or all of the following:
antidegradants, antioxidants, fatty acids, waxes, stearic acid and zinc oxide. Examples
of antidegradants and antioxidants include 6PPD, 77PD, IPPD and TMQ and may be added
to rubber compositions in an amount, for example, of from 0.5 phr and 5 phr. Zinc
oxide may be added in an amount, for example, of between 1 phr and 6 phr or alternatively,
of between 1.5 phr and 4 phr. Waxes may be added in an amount, for example, of between
1 phr and 5 phr.
[0063] The rubber compositions that are embodiments of the present invention may be produced
in suitable mixers, in a manner known to those having ordinary skill in the art, typically
using two successive preparation phases, a first phase of thermo-mechanical working
at high temperature, followed by a second phase of mechanical working at lower temperature.
[0064] The first phase of thermo-mechanical working (sometimes referred to as "non-productive"
phase) is intended to mix thoroughly, by kneading, the various ingredients of the
composition, with the exception of the vulcanization system. It is carried out in
a suitable kneading device, such as an internal mixer or an extruder, until, under
the action of the mechanical working and the high shearing imposed on the mixture,
a maximum temperature generally between 120° C and 190° C is reached.
[0065] After cooling of the mixture, a second phase of mechanical working is implemented
at a lower temperature. Sometimes referred to as "productive" phase, this finishing
phase consists of incorporating by mixing the vulcanization (or cross-linking) system,
i.e., the peroxide curing agent (coagents may be added in first phase), in a suitable device,
for example an open mill. It is performed for an appropriate time (typically for example
between 1 and 30 minutes) and at a sufficiently low temperature lower than the vulcanization
temperature of the mixture, so as to protect against premature vulcanization.
[0066] The rubber composition can be formed into useful articles, including treads for use
on vehicle tires and in particular embodiments for tire treads for use on passenger
cars and/or light trucks. The treads may be formed as tread bands and then later made
a part of a tire or they be formed directly onto a tire carcass by, for example, extrusion
and then cured in a mold. As such, tread bands may be cured before being disposed
on a tire carcass or they may be cured after being disposed on the tire carcass. Typically
a tire tread is cured in a known manner in a mold that molds the tread elements into
the tread, including,
e.g., the grooves, ribs and/or blocks molded into the tread.
[0067] As is known to those skilled in the art, tires treads may be constructed in a layered
form, such as a cap and base construction, wherein the cap is formed of one rubber
composition and the base is formed in another rubber composition. It is recognized
that in such tread constructions, the disclosed rubber compositions are useful for
that part of the tread that actually makes contact with the running surface,
e.g., the road surface.
[0068] It should be noted that the foregoing included detailed references to particular
embodiments of the present invention, which were provided by way of explanation of
the invention. For example, features illustrated or described as part of one embodiment
can be used with another embodiment to yield still a third embodiment. The invention
is further illustrated by the following examples, which are to be regarded only as
illustrations and not delimitative of the invention in any way. The properties of
the compositions disclosed in the examples were evaluated as described below and these
methods are suitable for measurement of the claimed properties of the present invention.
[0069] Modulus of elongation (MPa) was measured at 10% (MA10), 100% (MA100) and 300% (MA300)
at a temperature of 23 °C based on ASTM Standard D412 on dumb bell test pieces. The
measurements were taken in the second elongation;
i.e., after an accommodation cycle. These measurements are secant moduli in MPa, based
on the original cross section of the test piece.
[0070] Wet braking for a tire mounted on an automobile fitted with an ABS braking system
was determined by measuring the distance necessary to go from 50 MPH to 0 MPH upon
sudden braking on wetted ground (asphalt concrete) having a controlled water depth
of about 1.2 mm. A value greater than that of the control, which is arbitrarily set
to 100, indicates an improved result, that is to say a shorter wet braking distance.
[0071] Damp braking for a tire mounted on an automobile fitted with an ABS braking system
was determined by measuring the distance necessary to go from 50 MPH to 0 MPH upon
sudden braking on wetted ground (asphalt concrete) where the water depth did not exceed
the track surface roughness. A value greater than that of the control, which is arbitrarily
set to 100, indicates an improved result, that is to say a shorter wet braking distance.
[0072] Dry braking of a tire mounted on an automobile fitted with an ABS braking system
was measured by determining the distance necessary to go from 60 mph to a complete
stop upon sudden braking on a dry asphalt surface. A value greater than that of the
control, which is arbitrarily set to 100, indicates an improved result,
i.e., a shorter braking distance and improved dry grip.
[0073] Snow grip (%) on snow-covered ground was evaluated by measuring the forces on a single
driven test tire in snow according to the ASTM F1805 test method. The vehicle travels
at a constant 5 mph speed and the forces are measured on the single test tire at the
target slip. A value greater than that of the Standard Reference Test Tire (SRTT),
which is arbitrarily set to 100, indicates an improved result,
i.e., improved grip on snow.
[0074] Dynamic properties (Tg and G*) for the rubber compositions were measured on a Metravib
Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response
of a sample of vulcanized material (double shear geometry with each of the two 10
mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected
to an alternating single sinusoidal shearing stress of a constant 0.7 MPa and at a
frequency of 10 Hz over a temperature sweep from -60 °C to 100 °C with the temperature
increasing at a rate of 1.5 °C/min. The shear modulus G* at 60 °C was captured and
the temperature at which the max tan delta occurred was recorded as the glass transition
temperature, Tg.
Example 1
[0075] This example provides a demonstration of the improvement in wet and damp braking
performance, some improvement in dry braking performance while maintaining rolling
resistance.
[0076] Rubber compositions were prepared using the components shown in Table
1. The amount of each component making up these rubber compositions are provided in
parts per hundred parts of rubber by weight (phr).
[0077] The resin was the C5-C9 resin Oppera 373N available from ExxonMobil and having a
z average molecular weight greater than 20,000, a weight average molecular weight
of about 2500, a softening point of about 89 °C and has a glass transition temperature
of about 39 ° C. The plasticizing oil was AGRI-PURE 80 and the antidegradants included
wax and 6PPD. The SBR was a functionalized SBR having
trans-1,4 content of 38.1 wt. % functionalized at chain ends with a silanol group. The
silica coupling agent was Si69 in all rubber formulations except F
5, which used Si266 instead. As noted above, Si69 is a tetrasulfide silane while Si266
is a disulfide silane, both available from Evonik. The silica was Zeosil 1165MP or
Zeosil 165GR or a blend of the two for all the rubber formulations.
Table
1 - Rubber Formulations
Formulations |
W1 |
F1 |
F2 |
F3 |
F4 |
W2 |
F4 |
F5 |
SBR |
75 |
75 |
75 |
75 |
57 |
57 |
57 |
57 |
BR |
25 |
25 |
25 |
25 |
43 |
43 |
43 |
43 |
Carbon Black, N234 |
4 |
4 |
4 |
4 |
7 |
7 |
7 |
7 |
Silica |
120 |
120 |
120 |
120 |
104 |
104 |
104 |
104 |
Si69 |
9.6 |
9.6 |
9.6 |
9.6 |
7.8 |
7.8 |
7.8 |
|
Si266 |
|
|
|
|
|
|
|
6.9 |
Oil |
27 |
27 |
27 |
27 |
14 |
16 |
14 |
14 |
Resin |
55 |
55 |
55 |
55 |
38 |
41 |
38 |
38 |
Antidegradants, Processing Aids, Activators |
11 |
11 |
11 |
11 |
11 |
11 |
11 |
11 |
Sulfur |
1.4 |
|
|
|
|
1.1 |
|
|
CBS |
1.6 |
|
|
|
|
1.75 |
|
|
VULCUP R * |
|
3.5 |
3 |
3 |
4 |
|
4 |
4 |
Non-ionic Coagent |
|
|
4 |
|
|
|
|
|
Polar Coagent |
|
|
|
4 |
|
|
|
|
|
|
|
|
|
|
|
|
|
Physical Properties |
|
|
|
|
|
|
|
|
Shear Modulus G*60 @ 60 °C & 0.7 MPa |
0.72 |
0.76 |
0.70 |
0.67 |
0.99 |
1.1 |
0.99 |
1.1 |
Tg, °C |
-24 |
-25 |
-25 |
-25 |
-23 |
-21 |
-23 |
-19 |
MA10 @ 23 °C, MPa |
3.61 |
3.78 |
3.70 |
3.71 |
5.5 |
5.1 |
5.5 |
5.4 |
MA100 @ 23 °C, MPa |
0.91 |
0.89 |
0.83 |
0.85 |
1.0 |
1.2 |
1.0 |
1.2 |
MA300 @ 23 °C, MPa |
0.77 |
0.76 |
0.70 |
0.72 |
0.8 |
1.1 |
0.8 |
1.1 |
*Peroxide component contained only 40% active peroxide |
[0078] The non-ionic coagent in F
2 was RICON 153 (85% 1, 2 vinyl polybutadiene) and in F
3 it was a triallyl cyanurate (the allyl being a 1-propene moiety). The peroxide curing
agent was VULCUP R, which includes 60% non-active ingredients so that the amount of
active peroxide was 1.4 phr of active peroxide for F
1 and 1.2 phr of active peroxide for F
2 and F
3.
[0079] The rubber formulations were prepared by mixing the components given in Table
1, except for the peroxide or sulfur and the coagents or accelerators, in a Banbury
mixer by the process described above. The vulcanization package was added in the second
phase on a mill. Vulcanization was effected (25 minutes at 170°C) and the formulations
were then tested to measure their physical properties as reported in Table
1.
Example 2
[0080] Tires (P205/55R16 all-season variety) were manufactured using the rubber compositions
shown in Table
1 to form the treads. The tires were tested for their wet braking, dry braking and
snow traction in accordance with the test procedures described above. The test results
are shown in Table
2. All tire test results were normalized against the tires manufactured with the formulation
W1.
Table
2 - Tire Results
|
W1 |
F1 |
F2 |
F3 |
W2 |
F4 |
F5 |
Wet Braking |
100 |
102.6 |
102.5 |
103.2 |
100 |
102 |
111 |
Damp Braking |
100 |
108.5 |
109.9 |
111.8 |
100 |
105 |
- |
Dry Braking |
100 |
100.9 |
99.3 |
99.2 |
100 |
102 |
102 |
Snow Traction |
100 |
101.9 |
99.9 |
101.6 |
- |
- |
- |
[0081] As can be seen in Table
2, each of the tire treads manufactured with the rubber compositions F
1-F
3 provided improved wet braking, damp braking and snow traction over the witness. Dry
braking decreased with the use of the co-agent although the tires having treads that
included the coagent had improved damp braking performance.
[0082] Notably, even though tire tests were not run for damp braking or snow traction as
indicated in Table
2 W
2, F
4 and F
5, the significant increase in wet braking was realized for the tires having treads
made from formulation F
5 when the disulfide coupling agent was used instead of the tetrasulfide coupling agent.
It is apparent that improvements in the grip properties of the tires can be improved
when free sulfur is not introduced into the rubber mixture from the silane coupling
agent by using coupling agents having limited amounts of sulfur.
[0083] The terms "comprising," "including," and "having," as used in the claims and specification
herein, shall be considered as indicating an open group that may include other elements
not specified. The term "consisting essentially of," as used in the claims and specification
herein, shall be considered as indicating a partially open group that may include
other elements not specified, so long as those other elements do not materially alter
the basic and novel characteristics of the claimed invention. The terms "a," "an,"
and the singular forms of words shall be taken to include the plural form of the same
words, such that the terms mean that one or more of something is provided. The terms
"at least one" and "one or more" are used interchangeably. The term "one" or "single"
shall be used to indicate that one and only one of something is intended. Similarly,
other specific integer values, such as "two," are used when a specific number of things
is intended. The terms "preferably," "preferred," "prefer," "optionally," "may," and
similar terms are used to indicate that an item, condition or step being referred
to is an optional (not required) feature of the invention. Ranges that are described
as being "between a and b" are inclusive of the values for "a" and "b."
[0084] It should be understood from the foregoing description that various modifications
and changes may be made to the embodiments of the present invention without departing
from its true spirit. The foregoing description is provided for the purpose of illustration
only and should not be construed in a limiting sense. Only the language of the following
claims should limit the scope of this invention.
1. Lauffläche für einen Reifen, wobei die Lauffläche eine Kautschukzusammensetzung umfasst,
die auf einer vernetzbaren Elastomerzusammensetzung basiert, wobei die vernetzbare
Kautschukzusammensetzung pro 100 Gewichtsteile Kautschuk (phr) Folgendes umfasst:
100 phr von zwei Elastomerarten, die mindestens 50 phr eines Styrol-Butadien-Copolymers
(SBR) und als Rest ein Polybutadien (BR) enthalten;
zwischen 90 phr und 150 phr eines Siliciumdioxidfüllstoffs;
einen Organosilan-Haftvermittler;
eine wirksame Menge eines Plastifiziersystems, das ein weichmachendes Harz mit einer
Glasübergangstemperatur (Tg) von mindestens 25°C und eine weichmachende Flüssigkeit
enthält, wobei die wirksame Menge des Plastifiziersystems der Kautschukzusammensetzung
einen bei 60°C gemessenen Schermodul G* zwischen 0,6 MPa und 1,5 MPa und eine Tg zwischen
-35°C und 0°C verleiht;
ein Peroxid-Härtungsmittel.
2. Lauffläche nach Anspruch 1, wobei es sich bei dem Organosilan-Haftvermittler um einen
oder mehrere handelt, die aus der aus Organosilan-Haftvermittlern ohne Schwefelanteil
und mit einem Tetrasulfid-, Trisulfid-, Disulfid- und Mercapto-Anteil bestehenden
Gruppe ausgewählt sind.
3. Lauffläche nach Anspruch 1, wobei es sich bei dem Organosilan-Haftvermittler um einen
oder mehrere handelt, die aus der aus Organosilan-Haftvermittlern ohne Schwefel und
mit einem Disulfid und einem Mercapto bestehenden Gruppe ausgewählt sind.
4. Lauffläche nach Anspruch 1, wobei es sich bei dem Organosilan-Haftvermittler um einen
oder mehrere handelt, die aus der aus 3-Mercaptopropyltrimethoxysilan, 2-Mercaptoethyltrimethoxysilan
und 2-Mercaptodimethylmethoxysilan bestehenden Gruppe ausgewählt sind.
5. Lauffläche nach Anspruch 1, wobei es sich bei dem Organosilan-Haftvermittler um einen
oder mehrere handelt, die aus der aus 3-Glycidoxypropylmethyldimethoxysilan, Vinyltrimethoxysilan
und 3-Methacryloxypropylmethyldimethoxysilan bestehenden Gruppe ausgewählt sind.
6. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die vernetzbare Kautschukzusammensetzung
zwischen 10 phr und 30 phr der weichmachenden Flüssigkeit umfasst.
7. Lauffläche nach einem der vorhergehenden Ansprüche, wobei es sich bei der weichmachenden
Flüssigkeit um Pflanzenöl mit einem Ölsäuregehalt von mindestens 70 Gew.-% handelt.
8. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die wirksame Menge des Plastifiziersystems
der Kautschukzusammensetzung den bei 60°C gemessenen Schermodul G* zwischen 0,65 MPa
und 1,1 MPa verleiht.
9. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die wirksame Menge des Plastifiziersystems
der Kautschukzusammensetzung die Tg zwischen -30°C und -17°C verleiht.
10. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die vernetzbare Kautschukzusammensetzung
zwischen 95 phr und 145 phr Siliciumdioxid umfasst.
11. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die vernetzbare Kautschukzusammensetzung
zwischen 0,8 phr und 2,4 phr des Peroxid-Härtungsmittels umfasst.
12. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die vernetzbare Kautschukzusammensetzung
ferner ein nichtionisches Härtungs-Coagens umfasst.
13. Lauffläche nach Anspruch 12, wobei das nichtionische Härtungs-Coagens aus Allylcyanuraten,
Allylisocyanuraten, Phthalaten oder Kombinationen davon ausgewählt ist.
14. Lauffläche nach einem der Ansprüche 1 bis 12, wobei das nichtionische Härtungs-Coagens
aus einem Vinyl-SBR-Copolymer oder einem Vinyl-BR ausgewählt ist, wobei das Coagens
mindestens 70% Vinyl darstellt.
15. Lauffläche nach einem der vorhergehenden Ansprüche, wobei die vernetzbare Kautschukzusammensetzung
kein polares Härtungs-Coagens enthält.
1. Bande de roulement pour pneumatique, laquelle bande de roulement comprend une composition
de caoutchouc à base d'une composition d'élastomère réticulable, laquelle composition
de caoutchouc réticulable comprend, pour cent parties en poids de caoutchouc (pcpc)
:
- 100 pcpc d'élastomères de deux types, soit au moins 50 pcpc d'un copolymère de styrène
et de butadiène (SBR), et un polybutadiène (BR) pour le restant,
- entre 90 et 150 pcpc de silice, en tant que charge,
- un agent de couplage de type organo-silane,
- une quantité efficace d'un système plastifiant qui contient une résine plastifiante
présentant une température de transition vitreuse (Tv) d'au moins 25 °C et un liquide
plastifiant, laquelle quantité efficace de ce système plastifiant confère à la composition
de caoutchouc un module de cisaillement G*, mesuré à 60 °C, de 0,6 à 1,5 MPa, et une
température Tv située entre -35 et 0 °C,
- et un agent durcisseur de type peroxyde.
2. Bande de roulement conforme à la revendication 1, dans laquelle l'agent de couplage
de type organo-silane est un ou plusieurs de tels agents, choisi(s) dans l'ensemble
constitué par des agents de couplage de type organo-silane sans soufre, un tétrasulfure,
un tri-sulfure, un disulfure et un mercaptan.
3. Bande de roulement conforme à la revendication 1, dans laquelle l'agent de couplage
de type organo-silane est un ou plusieurs de tels agents, choisi(s) dans l'ensemble
constitué par des agents de couplage de type organo-silane sans soufre, un disulfure
et un mercaptan.
4. Bande de roulement conforme à la revendication 1, dans laquelle l'agent de couplage
de type organo-silane est un ou plusieurs de tels agents, choisi(s) dans l'ensemble
constitué par les suivants : 3-mercaptopropyl-triméthoxy-silane, 2-mercaptoéthyl-triméthoxy-silane,
et 2-mercapto-dimethyl-méthoxy-silane.
5. Bande de roulement conforme à la revendication 1, dans laquelle l'agent de couplage
de type organo-silane est un ou plusieurs de tels agents, choisi(s) dans l'ensemble
constitué par les suivants : 3-glycidyloxypropyl-méthyl-diméthoxy-silane, vinyl-triméthoxy-silane,
et 3-méthacryloxypropyl-méthyl-diméthoxy-silane.
6. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la composition de caoutchouc réticulable comprend entre 10 et 30 pcpc du liquide plastifiant.
7. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
le liquide plastifiant est une huile végétale dont la teneur en acide oléique vaut
au moins 70 % en poids.
8. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la quantité efficace de système plastifiant confère à la composition de caoutchouc
un module de cisaillement G*, mesuré à 60 °C, de 0,65 à 1,1 MPa.
9. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la quantité efficace de système plastifiant confère à la composition de caoutchouc
une température Tv située entre -30 et -17 °C.
10. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la composition de caoutchouc réticulable comprend entre 95 et 145 pcpc de silice.
11. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la composition de caoutchouc réticulable comprend entre 0,8 et 2,4 pcpc d'agent durcisseur
de type peroxyde.
12. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la composition de caoutchouc réticulable comprend en outre un co-agent durcisseur
non-ionique.
13. Bande de roulement conforme à la revendication 12, dans laquelle le co-agent durcisseur
non-ionique est choisi parmi les cyanurates d'allyle, isocyanurates d'allyle, phtalates
et leurs combinaisons.
14. Bande de roulement conforme à l'une des revendications 1 à 12, dans laquelle le co-agent
durcisseur non ionique est choisi parmi un copolymère SBR à groupes vinyle et un polymère
BR à groupes vinyle, et ce co-agent contient au moins 70 % de groupes vinyle.
15. Bande de roulement conforme à l'une des revendications précédentes, dans laquelle
la composition de caoutchouc réticulable ne contient pas de co-agent durcisseur polaire.